Magnetic Properties of Aucore-Coshell Nanoparticles

Au core -Co shell nanoparticles were synthesized by a wet-chemical method, and their magnetic properties were characterized. By comparing the blocking temperature of Au core -Co shell nanoparticles to pure cobalt nanoparticles of the same size, it is proposed that cobalt spins in the shell are all aligned by exchange interaction to form single domain nano shells. At the same time, a demagnetizing field in the gold core develops and is aligned along the magnetization direction of the cobalt shell. A greatly enhanced coercivity of Au core -Co shell nanoparticles at 10 K, compared to the pure cobalt sample, was observed. We propose that the enhanced coercivity of Au core -Co shell nanoparticles is due to the pinning effect of cobalt spins at the Au/Co interface. The pinning mechanisms include strain pinning and demagnetizing field pinning.